1. Field of the Invention
This invention relates to a serial type printing device to print characters and symbols on a recording sheet by shifting a character wheel (or ring) along the direction of a printing line. More particularly, it is concerned with a printing device capable of performing dichromatic printing using ink rollers of different colors.
2. Description of the Prior Art
There has so far been known a printing device of a type capable of printing characters and symbols on plain paper, such as one installed in an electronic desk top calculator, for example, wherein the character printing is done discretely in black in the case of addition and in red in the case of subtraction for the purpose of distinguishing the printed data. In such dichromatic printing device, however, ink ribbons (or tapes) are used in most cases, which inevitably requires a very large driving implement for the ink ribbons, hence overall dimension of the printing device increases. In addition, there is further necessity for providing a separate driving source for driving the ink ribbons, which disadvantageously increases the electric power consumption of the printing device.
As the measures for minimizing increase in the size of the printing device and the power consumption, there has been proposed an ink roller type printing device, in which an ink-impregnated roller is caused to contact with a character wheel, and, by its associated rotation with wheel, ink is applied onto the type faces arranged on the peripheral surface of the character wheel, after which the character wheel is hit by a hammer or other percussion device to print a character on a recording sheet.
According to this ink roller type printing device, no separate device needs be provided for driving the ink roller, and, moreover, impact force of the hammer can be reduced by making the type faces on the character wheel of an elastic material, whereby the power consumption can be curtailed. However, when the dichromatic printing is to be done by this ink roller type printing device as in the case of the abovementioned ink ribbon type printing device, difficulty is accompanied due to direct application of ink onto the type faces. In addition, an electronic appliance equipped with such ink roller type printing device for dichromatic printing is forced to be in a large size from the standpoint of its design specification.